Fragile X syndrome (FXS) represents the most common form of inherited cause of intellectual disability and the most frequent monogenic cause of autism spectrum disorder. As a result of a trinucleotide (CGG) expansion, the FMR1 gene is silenced and makes little or no FMR1 protein (FMRP). FMRP is an RNA-binding protein that negatively regulates protein synthesis. The loss of FMRP causes neurodevelopmental deficits and alterations in cerebral metabolism. ACT01 is a novel precision small molecule candidate drug inhibiting only the activity of dopamine transporter. In behavioral studies, administration of ACT01 restored phenotype behaviors of FMR1-null animals back to their wild type littermates. The outcomes of these experiments for the first time substantiate the possible links of abnormal behavior phenotypes, to reduced extracellular dopamine or dopamine deficiency, to excessive dopamine transporter activity, and to abnormal metabolism. These outcomes further suggest that ACT01 is a viable therapeutic candidate for FXS. DRI Biosciences intends to develop ACT01 toward FXS clinical use. The aim of the phase I proposal examines the effect of dopamine reuptake inhibition on 1) mediations of insulin secretion, 2) membrane protein presentation, and 3) the activities of the insulin signal transduction pathways. The entire body of research (Phase I/II) examines the effects (efficacy) of ACT01 on FXS pathophysiology and biochemistry, which will ultimately generate not only a useful medication but also a more relevant, translatable, and objective efficacy biomarker as an adjunct to the behavior assessments in human clinic.